Pneumatic tire and method for manufacturing pneumatic tire

ABSTRACT

A belt cover layer is formed by spirally winding belt cover materials including a first cover material and a second cover material. When one side in a tire width direction with respect to a tire equatorial plane is defined as a first side and another side is defined as a second side, the first cover material is disposed from a position between a shoulder region on the second side and the tire equatorial plane to a shoulder region on the first side. The second cover material is disposed from a position between the shoulder region (Ash) on the first side and the tire equatorial plane to the shoulder region on the second side. The first cover material and the second cover material have an overlapping portion at a position where positions in the tire width direction become positions identical to one another.

TECHNICAL FIELD

The present technology relates to a pneumatic tire, and a method formanufacturing a pneumatic tire.

BACKGROUND ART

Some pneumatic tires in the related art have achieved desiredperformance by devising a member disposed on an outer side in a tireradial direction of a belt layer. For example, a pneumatic tiredescribed in Japan Patent No. 4865259 improves projection resistance insuch a way that two belt protecting layers are disposed on an outer sidein a tire radial direction of a belt layer, and the belt protectinglayer on the outer side in the tire radial direction has a narrowerwidth than a width of the belt protecting layer on an inner side in thetire radial direction. In a pneumatic tire described in Japan UnexaminedPatent Publication No. 2010-64644, a belt reinforcing layer is disposedbetween a tread portion and a belt layer, and the belt reinforcing layeris configured to be three layers on a tire equatorial portion to ensurebreaking energy while suppressing an increase in weight.

A pneumatic tire described in Japan Unexamined Patent Publication No.2017-137032 includes a band-like sound absorbing member adhered to atire inner surface in a tread portion, a full cover layer disposed on anouter circumferential side of a belt layer, and a center cover layerdisposed on an outer circumferential side of the full cover layer andlocally covering a tire width central region. Defining respective widthof the band-like sound absorbing member and the belt layer and width ofthe center cover layer and the band-like sound absorbing member reducesa decrease in high-speed durability due to accumulation of heat in theband-like sound absorbing member while obtaining sufficient quietness bythe band-like sound absorbing member.

In a pneumatic tire described in Japan Patent No. 4635366, a belt coverlayer constituted by an end portion belt cover layer and a centralportion belt cover layer is disposed outside a belt layer, and a tensilestrength of organic fiber cords forming the end portion belt cover layerand the central portion belt cover layer and a sum of the end portionbelt cover layer and the central portion belt cover layer are defined toensure reduction in road noise in a high frequency band and weightreduction. Additionally, a pneumatic tire described in Japan Patent No.4687201 includes a belt cover formed by spirally winding a stripmaterial on an outer circumferential side of a belt layer. In the beltcover, lap winding of the strip material at a position covering an endportion in a tire width direction in the belt layer and a positioncovering a central portion in the tire width direction in the belt layerimproves steering stability and durability.

Here, among pneumatic tires, for example, there are pneumatic tires thatcan accommodate a high load, such as a pneumatic tire with EXTRA LOADstandard. Such pneumatic tires can be used at relatively high airpressures for accommodating high loads. Meanwhile, when the air pressureof the pneumatic tire is increased, rigidity of a tread portionincreases. As a result, the tread portion is less likely to deform whena foreign material is trodden, and a shock burst, which occurs caused bythe tread of the foreign material, is likely to occur. That is, the useof the pneumatic tire at high air pressure is likely to reduce shockburst resistance performance, which is a resistance against a shockburst.

A shock burst is likely to occur by treading a foreign material on aroad surface in a region at or near a tire equatorial plane on a groundcontact surface of the tread portion. Accordingly, to improve shockburst resistance performance, reinforcement in the vicinity of the tireequatorial plane in the tread portion is effective. However, newaddition of a member for reinforcement increases a manufacturing processby that much, thereby reducing productivity. Accordingly, improvingproductivity while suppressing a decrease in shock burst resistanceperformance has been extremely difficult.

SUMMARY

The present technology provides a pneumatic tire that allows improvingproductivity while suppressing a decrease in shock burst resistanceperformance and a method for manufacturing the pneumatic tire.

A pneumatic tire according to an embodiment of the present technologyincludes a tread portion, a belt layer, and a belt cover layer. The beltlayer is disposed in the tread portion. The belt cover layer is disposedon an outer side in a tire radial direction of the belt layer. The beltcover layer is formed by spirally winding band-like belt cover materialson the outer side of the belt layer in the tire radial direction arounda tire rotation axis. The belt cover materials include a first covermaterial and a second cover material. When one side in a tire widthdirection with respect to a tire equatorial plane is defined as a firstside and another side in the tire width direction with respect to thetire equatorial plane is defined as a second side, the first covermaterial is disposed from a position between a shoulder region on thesecond side and the tire equatorial plane to a shoulder region on thefirst side. The second cover material is disposed from a positionbetween the shoulder region on the first side and the tire equatorialplane to the shoulder region on the second side. The first covermaterial and the second cover material have an overlapping portion at aposition where positions in the tire width direction become positionsidentical to one another. The first cover material and the second covermaterial overlap in the tire radial direction at the overlappingportion. The overlapping portion has a width in the tire width directionthat varies depending on a position thereof in a tire circumferentialdirection.

In the pneumatic tire, the overlapping portion preferably has a minimumwidth of the width in the tire width direction of not less than 5 mm.The overlapping portion preferably has a maximum width of the width inthe tire width direction of not greater than 40 mm.

In the pneumatic tire, the belt cover materials are preferably foldedback in the tire radial direction at the shoulder regions.

In the pneumatic tire, the belt cover materials preferably have a widthin the tire width direction of portions overlapping in the tire radialdirection of within a range of from not less than 5% to not greater than50% of a width in the tire width direction of the belt cover layer.

In the pneumatic tire, the belt cover material preferably includes anadjacent wrap portion where portions adjacent in the tire widthdirection overlap in the tire radial direction by the spiral winding.The adjacent wrap portion preferably has a width in the width directionof the belt cover materials in a range of from not less than 20% to notgreater than 70% of a width of the belt cover materials.

In the pneumatic tire, at least one of the first cover material or thesecond cover material preferably includes the adjacent wrap portion suchthat the overlapping portion has a portion where the belt covermaterials are three or more layers.

In the pneumatic tire, the first cover material and the second covermaterial preferably are an identical type.

A method for manufacturing a pneumatic tire according to an embodimentof the present technology spirally winds band-like belt cover materialson an outer side in a tire radial direction of a belt layer around atire rotation axis to dispose a belt cover layer. The method includes:using a first cover material and a second cover material as the beltcover materials; when one side in a tire width direction with respect toa tire equatorial plane is defined as a first side and another side inthe tire width direction with respect to the tire equatorial plane isdefined as a second side, spirally winding the first cover material froma position between a shoulder region on the second side and the tireequatorial plane to a shoulder region on the first side; and spirallywinding the second cover material from a position between the shoulderregion on the first side and the tire equatorial plane to the shoulderregion on the second side. Winding the first cover material and windingthe second cover material overlap the first cover material and thesecond cover material in the tire radial direction at a portion wherepositions in the tire width direction are an identical position betweenthe first cover material and the second cover material to form anoverlapping portion. The overlapping portion has a width in the tirewidth direction that varies depending on a position thereof in a tirecircumferential direction. The first cover material and the second covermaterial overlap in the tire radial direction at the overlappingportion.

In the method for manufacturing the pneumatic tire, the winding of thefirst cover material preferably spirally winds the first cover materialfrom the position between the shoulder region on the second side and thetire equatorial plane to the shoulder region on the first side. Thewinding of the second cover material preferably spirally winds thesecond cover material from the position between the shoulder region onthe first side and the tire equatorial plane to the shoulder region onthe second side.

The pneumatic tire and the method for manufacturing the pneumatic tireaccording to the embodiment of the present technology provide an effectthat allows improving productivity while suppressing a decrease in shockburst resistance performance.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a meridian cross-sectional view illustrating a main portion ofa pneumatic tire according to a first embodiment.

FIG. 2 is a detailed view of a tread portion illustrated in FIG. 1.

FIG. 3 is a schematic diagram of a belt cover layer in a direction ofthe arrow A-A in FIG. 2.

FIG. 4 is a detailed view of a center land portion illustrated in FIG.2.

FIG. 5 is a schematic view describing directions in which a first covermaterial and a second cover material are wound.

FIG. 6 is an explanatory diagram illustrating a state in which aprojection on a road surface is trodden by the pneumatic tire accordingto the first embodiment.

FIG. 7 is a schematic view of a first cover material and a second covermaterial of a pneumatic tire according to a second embodiment.

FIG. 8 is a schematic view of belt cover materials included in apneumatic tire according to a third embodiment.

FIG. 9 is a plan view of the belt cover material illustrated in FIG. 8.

FIG. 10 is a modified example of the third embodiment, and is anexplanatory diagram in a case where the belt cover material is foldedback at shoulder regions.

FIG. 11 is a modified example of the first embodiment, and is anexplanatory diagram in a case where a full cover is provided outside anoverlapping portion.

FIGS. 12A-12B include a table showing results of performance evaluationtests of pneumatic tires.

DETAILED DESCRIPTION

Embodiments of a pneumatic tire and a method for manufacturing apneumatic tire according to embodiments of the present technology willbe described in detail below with reference to the drawings. However,the present technology is not limited by the embodiment. Constituents ofthe following embodiments include elements that are essentiallyidentical or that can be substituted or easily conceived of by a personskilled in the art.

First Embodiment Pneumatic Tire

Herein, “tire radial direction” refers to the direction orthogonal tothe rotation axis (not illustrated) of a pneumatic tire 1. “Inner sidein the tire radial direction” refers to the direction toward therotation axis in the tire radial direction. “Outer side in the tireradial direction” refers to the direction away from the rotation axis inthe tire radial direction. Additionally, “Tire circumferentialdirection” refers to the circumferential direction with the rotationaxis as the center axis. Additionally, “tire width direction” refers toa direction parallel with the rotation axis. “Inner side in the tirewidth direction” refers to a side toward a tire equatorial plane (tireequator line) CL in the tire width direction. “Outer side in the tirewidth direction” refers to a side away from the tire equatorial plane CLin the tire width direction. “Tire equatorial plane CL” refers to aplane orthogonal to the tire rotation axis and extending through thecenter of the tire width of the pneumatic tire 1. The tire equatorialplane CL is aligned, in the tire width direction, with a tire widthdirection center line corresponding to the center position of thepneumatic tire 1 in the tire width direction. “Tire width” is the widthin the tire width direction between portions located on the outermostside in the tire width direction, or in other words, the distancebetween the portions that are the most distant from the tire equatorialplane CL in the tire width direction. “Tire equator line” refers to theline in the tire circumferential direction of the pneumatic tire 1 thatlies on the tire equatorial plane CL.

FIG. 1 is a meridian cross-sectional view illustrating a main portion ofthe pneumatic tire 1 according to a first embodiment. The pneumatic tire1 according to the present first embodiment is the pneumatic tire 1 thatcan accommodate use at high loads, for example, the pneumatic tire 1with EXTRA LOAD standard. In the pneumatic tire 1 according to thepresent first embodiment, a tread portion 2 is disposed on a portion onthe outermost side in the tire radial direction when viewed in ameridian cross-section, and the tread portion 2 includes a tread rubberlayer 4 made of a rubber composition. A surface of the tread portion 2,that is, a portion in contact with a road surface during traveling of avehicle (not illustrated) having the pneumatic tires 1 mounted thereonis formed as a ground contact surface 3, and the ground contact surface3 forms a part of a contour of the pneumatic tire 1. A plurality of maingrooves 30 extending in the tire circumferential direction are formed inthe ground contact surface 3 in the tread portion 2, and a plurality ofland portions 20 are defined by the plurality of main grooves 30 on thesurface of the tread portion 2. In the present first embodiment, fourmain grooves 30 are formed side by side in the tire width direction, andeach two of the four main grooves 30 are disposed on both sides in thetire width direction of the tire equatorial plane CL. In other words,the four main grooves 30 in total are formed in the tread portion 2,including: two center main grooves 31 disposed on both sides of the tireequatorial plane CL; and two shoulder main grooves 32 disposed on anouter side in the tire width direction of each of the two center maingrooves 31.

Note that “main groove 30” refers to a vertical groove in which at leasta part is extending in the tire circumferential direction. In general,the main groove 30 has a groove width of not less than 3 mm and a groovedepth of not less than 6 mm and has a tread wear indicator (slip sign)therein, indicating terminal stages of wear. In the present firstembodiment, the main groove 30 has a groove width of not less than 6 mmand not greater than 25 mm and a groove depth of not less than 6 mm andnot greater than 9 mm and is substantially parallel to a tire equatorline (centerline) where the tire equatorial plane CL and the groundcontact surface 3 intersect. The main grooves 30 may extend linearly inthe tire circumferential direction or may be provided in a wave shape ora zigzag shape.

Among the land portions 20 defined by the main grooves 30, the landportion 20 positioned between the two center main grooves 31 andpositioned on the tire equatorial plane CL is a center land portion 21.Moreover, the land portions 20 positioned between the adjacent centermain grooves 31 and shoulder main grooves 32 and disposed on the outerside in the tire width direction of the center land portion 21 aresecond land portions 22. Moreover, the land portions 20 positioned onthe outer side in the tire width direction of the second land portions22 and adjacent to the second land portions 22 with the shoulder maingrooves 32 disposed therebetween are shoulder land portions 23.

Note that the land portions 20 may be formed in a rib shape across onecircumference in the tire circumferential direction, and a plurality oflug grooves (not illustrated) extending in the tire width direction maybe formed in the tread portion 2. Thus, the land portions 20 may bedefined by the main grooves 30 and the lug grooves, and each of the landportions 20 may be formed in a block shape. In the present firstembodiment, the land portion 20 is formed as the rib-shaped land portion20 formed across one circumference in the tire circumferentialdirection.

Shoulder portions 5 are positioned at both ends on outer sides of thetread portion 2 in the tire width direction, and sidewall portions 8 aredisposed on inner sides in the tire radial direction of the shoulderportions 5. In other words, the sidewall portions 8 are disposed on bothsides in the tire width direction of the tread portion 2. In otherwords, the sidewall portions 8 are disposed at two sections on bothsides in the tire width direction of the pneumatic tire 1 and formportions exposed to the outermost sides in the tire width direction ofthe pneumatic tire 1.

A bead portion 10 is located on an inner side in the tire radialdirection of each of the sidewall portions 8 located on both sides inthe tire width direction. Similarly to the sidewall portions 8, the beadportions 10 are disposed at two sections on both sides of the tireequatorial plane CL. That is, the bead portions 10 are disposed as apair on both sides in the tire width direction of the tire equatorialplane CL. Each bead portion 10 is provided with a bead core 11, and abead filler 12 is provided on an outer side in the tire radial directionof the bead core 11. The bead core 11 is an annular member formed in anannular shape by bundling bead wires, which are steel wires, and thebead filler 12 is a rubber member disposed on the outer side in the tireradial direction of the bead core 11.

A belt layer 14 is disposed in the tread portion 2. The belt layer 14 isformed by a multilayer structure in which a plurality of belts 141, 142are layered, and the two layers of the belts 141, 142 are layered in thepresent first embodiment. The belts 141, 142 constituting the belt layer14 are formed by rolling and covering, with coating rubber, a pluralityof belt cords made of steel or an organic fiber material, such aspolyester, rayon, or nylon, and a belt angle defined as an inclinationangle of the belt cords with respect to the tire circumferentialdirection is within a predetermined range (for example, from not lessthan 20° to not greater than 55°). Furthermore, the belt angles of thetwo layers of the belts 141, 142 differ from one another. Accordingly,the belt layer 14 is configured as a so-called crossply structure inwhich the two layers of the belts 141, 142 are layered with theinclination directions of the belt cords intersecting with one another.In other words, the two layers of the belts 141, 142 are provided asso-called cross belts in which the belt cords provided with therespective belts 141, 142 are disposed in mutually intersectingorientations.

A belt cover layer 15 is disposed on the outer side in the tire radialdirection of the belt layer 14. The belt cover layer 15 is disposed onthe outer side in the tire radial direction of the belt layer 14, coversthe belt layer 14 in the tire circumferential direction, and is providedas a reinforcing layer that reinforces the belt layer 14. The belt coverlayer 15 is formed by covering, with coating rubber, a plurality ofcords (not illustrated) disposed side by side in the tire widthdirection substantially parallel to the tire circumferential direction.The cords provided with the belt cover layer 15 are made of, forexample, steel or an organic fiber, such as polyester, polyethyleneterephthalate, rayon, nylon, and a hybrid of a polyamide composite +α,and a cord angle is within a range of ±5° with respect to the tirecircumferential direction. Moreover, in the cords provided with the beltcover layer 15, a wire diameter, which is a diameter of the cord, iswithin a range of from not less than 0.5 mm to not greater than 1.8 mm,and a cord count per 50 mm in an arrangement direction of the cords iswithin a range of from not less than 30 to not greater than 80. In thepresent first embodiment, the belt cover layer 15 is disposed across theentire region of the range in the tire width direction in which the beltlayer 14 is disposed and covers end portions in the tire width directionof the belt layer 14. The tread rubber layer 4 provided with the treadportion 2 is disposed on the outer side in the tire radial direction ofthe belt cover layer 15 in the tread portion 2.

A carcass layer 13 containing the cords of radial plies is continuouslyprovided on an inner side in the tire radial direction of the belt layer14 and on a side of the sidewall portion 8 close to the tire equatorialplane CL.

Accordingly, the pneumatic tire 1 according to the present firstembodiment is configured as a so-called radial tire. The carcass layer13 has a single layer structure made of one carcass ply or a multilayerstructure made of a plurality of carcass plies, and spans between thepair of bead portions 10 disposed on both sides in the tire widthdirection in a toroidal shape to form the framework of the tire.

Specifically, the carcass layer 13 is disposed to span from one beadportion 10 to the other bead portion 10 among the pair of bead portions10 located on both sides in the tire width direction and turns backtoward the outer side in the tire width direction along the bead cores11 at the bead portions 10 so as to wrap around the bead cores 11 andthe bead fillers 12. The bead filler 12 is a rubber member disposed in aspace formed on the outer side in the tire radial direction of the beadcore 11 when the carcass layer 13 is folded back at the bead portion 10.Moreover, the belt layer 14 is disposed on the outer side in the tireradial direction of a portion, located in the tread portion 2, of thecarcass layer 13 spanning between the pair of bead portions 10.Moreover, the carcass ply of the carcass layer 13 is made by rolling andcovering, with coating rubber, a plurality of carcass cords made fromsteel or an organic fiber material such as aramid, nylon, polyester, orrayon. The plurality of carcass cords that form the carcass ply aredisposed side by side with an angle in the tire circumferentialdirection, the angle with respect to the tire circumferential directionfollowing a tire meridian direction.

At the bead portion 10, a rim cushion rubber 17 is disposed on an innerside in the tire radial direction and an outer side in the tire widthdirection of the bead core 11 and a turned back portion of the carcasslayer 13, the rim cushion rubber 17 forming a contact surface of thebead portion 10 against the rim flange. Additionally, an innerliner 16is formed along the carcass layer 13 on the inner side of the carcasslayer 13 or on the inner side of the carcass layer 13 in the pneumatictire 1. The innerliner 16 forms a tire inner surface 18 that is asurface on the inner side of the pneumatic tire 1.

FIG. 2 is a detailed view of the tread portion 2 illustrated in FIG. 1.FIG. 3 is a schematic diagram of the belt cover layer 15 in a directionof the arrow A-A in FIG. 2. The belt cover layer 15 disposed on theouter side in the tire radial direction of the belt layer 14 is formedby spirally winding belt cover materials 40, which are band-like membersformed in a band shape, on the outer side in the tire radial directionof the belt layer 14 around the tire rotation axis. The belt covermaterial 40, which is the band-like member, has a width in a range offrom not less than 5 mm to not greater than 15 mm. The belt covermaterials 40 are reinforcing layer constituent members constituting thebelt cover layer 15, and a cord constituting the belt cover layer 15 isformed by being coated with a coating rubber.

The belt cover material 40 includes a first cover material 41 and asecond cover material 42. The first cover material 41 and the secondcover material 42 are each formed in a band shape, and are each spirallywound on the outer side outer side of the belt layer 14 in the tireradial direction. In addition, the first cover material 41 and thesecond cover material 42 are members of an identical type and are eachformed by coating the cords constituting the belt cover layer 15 withcoating rubbers. In other words, the first cover material 41 and thesecond cover material 42 have a configuration in which, for example,widths and thicknesses, wire diameters of the cords and intervals of thecords, and materials of the cords and the coating rubbers can beregarded as being identical.

Additionally, disposed positions of the first cover material 41 and thesecond cover material 42 in the tire width direction are disposed atsides opposite to one another with the tire equatorial plane CL as itscenter, and the first cover material 41 and the second cover material 42overlap at a position at or near the center in the tire width direction.Specifically, in a case where one side with respect to the tireequatorial plane CL in the tire width direction is defined as a firstside S1 and the other side with respect to the tire equatorial plane CLin the tire width direction is defined as a second side S2, the firstcover material 41 is disposed from a position between a shoulder regionAsh on the second side S2 and the tire equatorial plane CL to theshoulder region Ash on the first side S1. The second cover material 42is disposed from a position between the shoulder region Ash on the firstside S1 and the tire equatorial plane CL to the shoulder region Ash onthe second side S2.

Note that the shoulder region Ash in this case is a region between aposition P at 85% of the width of the belt layer 14 in the tire widthdirection and an end portion 144 of the belt layer 14 in the tire widthdirection. Specifically, in a tire meridian cross-section, the shoulderregion Ash is a region positioned between two shoulder region boundarylines Lsh. The shoulder region boundary lines Lsh are respective linesperpendicularly extending from the position P at 85% of the width of awidest belt 143 in the tire width direction, which has the widest widthin the tire width direction among the plurality of belts 141, 142provided with the belt layer 14, and the end portion 144 of the widestbelt 143 to the tire inner surface 18. The shoulder regions Ash thusdefined are defined on both sides of the tire equatorial plane CL in thetire width direction, and are positioned on respectively both sides ofthe tire equatorial plane CL in the tire width direction.

In the first present embodiment, of the two layers of the belts 141, 142included in the belt layer 14, a width of the belt 141 in the tire widthdirection positioned on the inner side in the tire radial direction iswider than a width of the other belt 142 in the tire width direction,and the belt 141 positioned on the inner side in the tire radialdirection is the widest belt 143.

Also, the positions P at 85% of the width of the widest belt 143 in thetire width direction are positions of end portions of a 85% region whena region of 85% of the width of the widest belt 143 in the tire widthdirection is evenly distributed on both sides in the tire widthdirection with the center of the widest belt 143 in the tire widthdirection or the position of the tire equatorial plane CL as the center.Accordingly, intervals between the positions P at 85% of the width ofthe widest belt 143 in the tire width direction and the end portions 144of the widest belt 143 are identical sizes between both sides of thetire equatorial plane CL in the tire width direction.

The shoulder region Ash defined in this manner is defined by a shape ina state in which the pneumatic tire 1 is mounted on a regular rim and isinflated to the regular internal pressure. Here, “regular rim” refers toa “standard rim” defined by JATMA (The Japan Automobile TyreManufacturers Association, Inc.), a “Design Rim” defined by TRA (TheTire and Rim Association, Inc.), or a “Measuring Rim” defined by ETRTO(The European Tyre and Rim Technical Organisation). Moreover, a regularinternal pressure refers to a “maximum air pressure” defined by JATMA,the maximum value in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATIONPRESSURES” defined by TRA, or “INFLATION PRESSURES” defined by ETRTO.

In addition, the first cover material 41 and the second cover material42 are each spirally wound on the outer side of the belt layer 14 in thetire radial direction. The direction of the spiral is a direction thatis symmetrical when viewed with the tire equatorial plane CL as itscenter. In other words, the first cover material 41 and the second covermaterial 42 have the identical winding direction in the tirecircumferential direction in heading from the tire equatorial plane CLside to the shoulder region Ash sides. Specifically, the direction ofwinding of the first cover material 41 in the tire circumferentialdirection in heading from the tire equatorial plane CL side to theshoulder region Ash side on the first side S1, and the direction ofwinding of the second cover material 42 in the tire circumferentialdirection in heading from the tire equatorial plane CL side to theshoulder region Ash side on the second side S2 are the identicaldirection.

Furthermore, the first cover material 41 and the second cover material42 have an overlapping portion 45 where the first cover material 41 andthe second cover material 42 overlap in the tire radial direction at aposition where positions in the tire width direction are identical toone another.

FIG. 4 is a detailed view of the center land portion 21 illustrated inFIG. 2. An inner end portion 41 a (see FIG. 3) as an end portion closeto the tire equatorial plane CL of the first cover material 41 ispositioned on the second side S2, and an inner end portion 42 a (seeFIG. 3) as an end portion close to the tire equatorial plane CL of thesecond cover material 42 is positioned on the first side S1. Theoverlapping portion 45 is formed at a position between a portion of thefirst cover material 41 positioned on the second side S2 and a portionof the second cover material 42 positioned on the first side S1. Thus,the overlapping portion 45 is formed so as to go across the tireequatorial plane CL in the tire width direction, and at least a part ofthe overlapping portion 45 is positioned on the inner side in the tireradial direction of the center land portion 21. In other words, whilethe first cover material 41 and the second cover material 42 are woundin one layer at the positions on the inner side in the tire radialdirection of the second land portion 22 and the shoulder land portion23, the two layers of the first cover material 41 and the second covermaterial 42 are overlappingly wound in the tire radial direction at theposition on the inner side in the tire radial direction of the centerland portion 21 and the portion where both of the first cover material41 and the second cover material 42 are disposed.

In other words, since the first cover material 41 and the second covermaterial 42 are spirally wound without overlapping the belt covermaterials 40 in the tire radial direction at the positions on the innerside in the tire radial direction of the second land portion 22 and theshoulder land portion 23, the belt cover material 40 is wound in onelayer. In contrast, when the first cover material 41 and the secondcover material 42 are each spirally wound at the position on the innerside in the tire radial direction of the center land portion 21 and atthe portion where both of the first cover material 41 and the secondcover material 42 disposed, both are overlappingly wound in the tireradial direction, and thus the belt cover materials 40 are wound in thetwo layers. The overlapping portion 45 is a portion where the largernumber of belt cover materials 40 is layered compared with that at theposition other than the overlapping portion 45 in a range in which thebelt cover layer 15 is disposed.

Thus, the first cover material 41 and the second cover material 42forming the overlapping portion 45 are disposed such that the positionof the inner end portion 41 a of the first cover material 41 in the tirecircumferential direction and the position of the inner end portion 42 aof the second cover material 42 in the tire circumferential directionare different positions.

Here, because the first cover material 41 and the second cover material42 are spirally disposed around the tire rotation axis, both areinclined in the tire width direction with respect to the tirecircumferential direction. Furthermore, the position of the inner endportion 41 a of the first cover material 41 in the tire circumferentialdirection differs from the position of the inner end portion 42 a of thesecond cover material 42 in the tire circumferential direction. Thus,the overlapping portion 45 formed by overlapping the first covermaterial 41 and the second cover material 42 in the tire radialdirection has a width W in the tire width direction that variesdepending on the position in the tire circumferential direction.

The overlapping portion 45 having the varying width W in the tire widthdirection has a minimum width Wmin (see FIG. 3), which is a width at aposition where the width W in the tire width direction is minimized, ofnot less than 5 mm, and a maximum width Wmax (see FIG. 3), which is awidth at a position where the width W in the tire width direction ismaximized, of not greater than 40 mm. In other words, the overlappingportion 45 has the width W in the tire width direction in a range offrom not less than 5 mm to not greater than 40 mm.

Method for Manufacturing Pneumatic Tire

Next, the manufacturing method for the pneumatic tire 1 according to thefirst embodiment will be described. To manufacture the pneumatic tire 1,first, processing is performed on each of the members constituting thepneumatic tire 1, and the processed members are assembled. That is, therubber members, such as the tread rubber layer 4, and the respectivemembers, such as the bead core 11, the carcass layer 13, the belt layer14, and the belt cover layer 15 are each processed and the processedmembers are assembled. Of these, the belt cover layer 15 is disposed onthe outer side in the tire radial direction of the belt layer 14 byspirally winding the band-like belt cover materials 40 on the outer sideof the belt layer 14 in the tire radial direction around the tirerotation axis.

As the belt cover materials 40, which are the members for forming thebelt cover layer 15, the first cover material 41 (see FIG. 3) and thesecond cover material 42 (see FIG. 3) are used in the present firstembodiment. A step of disposing the belt cover layer 15 on the outerside of the belt layer 14 in the tire radial direction includes: a stepof spirally winding the first cover material 41 from the positionbetween the shoulder region Ash on the second side S2 (see FIG. 2) andthe tire equatorial plane CL to the shoulder region Ash on the firstside S1 (see FIG. 2); and a step of spirally winding the second covermaterial 42 from the position between the shoulder region Ash on thefirst side Si and the tire equatorial plane CL to the shoulder regionAsh on the second side S2. That is, in the step of winding the firstcover material 41, while the inner end portion 41 a (see FIG. 3) of thefirst cover material 41 is positioned on the second side S2, the mostpart of the first cover material 41 is wound on the first side S1. Inthe step of winding the second cover material 42, while the inner endportion 42 a (see FIG. 3) of the second cover material 42 is positionedon the first side S1, the most part of the second cover material 42 iswound on the second side S2.

The step of winding the first cover material 41 and the step of windingthe second cover material 42 are performed with times overlapping withone another. In other words, at least a part of a work in the step ofwinding the first cover material 41 and at least a part of a work in thestep of winding the second cover material 42 in the step of winding thefirst cover material 41 and the step of winding the second covermaterial 42 are performed at the identical time.

In addition, the first cover material 41 and the second cover material42 are each wound such that the position of the inner end portion 41 aof the first cover material 41 in the tire circumferential direction andthe position of the inner end portion 42 a of the second cover material42 in the tire circumferential direction differ from one another. Thus,while the first cover material 41 and the second cover material 42 areeach spirally wound around the tire rotation axis on the outer side inthe tire radial direction of the belt layer 14, the first cover material41 and the second cover material 42 are disposed in the predeterminedrange, and thus the belt cover layer 15 is disposed on the outer side inthe tire radial direction of the belt layer 14.

Also, in the step of winding the first cover material 41 and the step ofwinding the second cover material 42, the first cover material 41 andthe second cover material 42 are overlapped in the tire radial directionat the portion where the positions in the tire width direction are theidentical position between the first cover material 41 and the secondcover material 42. In other words, in the step of winding the firstcover material 41 and the step of winding the second cover material 42,the first cover material 41 and the second cover material 42 overlap inthe tire radial direction at the position between the portion of thefirst cover material 41 positioned on the second side S2 and the portionof the second cover material 42 positioned on the first side S1. As aresult, the overlapping portion 45 where the first cover material 41 andthe second cover material 42 overlap in the tire radial direction isformed. At this time, in the step of winding the first cover material 41and the step of winding the second cover material 42, since both of thefirst cover material 41 and the second cover material 42 are spirallywound, the first cover material 41 and the second cover material 42 arewound to be inclined in the tire width direction with respect to thetire circumferential direction. In addition, the first cover material 41and the second cover material 42 are wound such that the position of theinner end portion 41 a of the first cover material 41 in the tirecircumferential direction and the position of the inner end portion 42 aof the second cover material 42 in the tire circumferential directiondiffer from one another. Accordingly, the overlapping portion 45 isformed in a configuration in which the width W in the tire widthdirection varies depending on the position in the tire circumferentialdirection.

FIG. 5 is a schematic view describing directions in which the firstcover material 41 and the second cover material 42 are wound. In thestep of winding the first cover material 41, the first cover material 41is spirally wound from the position between the shoulder region Ash onthe second side S2 and the tire equatorial plane CL to the shoulderregion Ash on the first side S1. Similarly, in the step of winding thesecond cover material 42, the second cover material 42 is spirally woundfrom the position between the shoulder region Ash on the first side S1and the tire equatorial plane CL to the shoulder region Ash on thesecond side S2. In other words, first, the inner end portion 41 a of thefirst cover material 41 is disposed on the second side S2 and spirallywound to the shoulder region Ash side on the first side S1. Similarly,first, the inner end portion 42 a of the second cover material 42 isdisposed on the first side S1 and spirally wound to the shoulder regionAsh side on the second side S2. In other words, the first cover material41 and the second cover material 42 are each wound to the outer side inthe tire width direction from the position near the tire equatorialplane CL.

Functions and Effects

To mount the pneumatic tire 1 according to the present first embodimenton a vehicle, a rim wheel R (see FIG. 6) is fitted to the bead portion10 to mount the pneumatic tire 1 on the rim wheel R, and then the innerportion is filled with air, and the rim wheel R is mounted on thevehicle with the pneumatic tire 1 in an inflated state. The orientationwhen the pneumatic tire 1 is mounted on the vehicle may be such that thefirst side S1 is on the inner side in the vehicle width direction andthe second side S2 is on the outer side in the vehicle width direction,or the first side S1 is on the outer side in the vehicle width directionand the second side S2 is on the inner side in the vehicle widthdirection. Note that in the pneumatic tire 1 in which the orientationwhen the pneumatic tire 1 is mounted on a vehicle is designated, therelationship between the inner side and the outer side in a vehiclemounting direction and the first side S1 and the second side S2 may bepreset.

The pneumatic tire 1 according to the present first embodiment is, forexample, the pneumatic tire 1 that can accommodate use at high loads,such as the pneumatic tire 1 with EXTRA LOAD standard. As such, thepneumatic tire 1 can be used with an air pressure at inflation in arelatively high state. Thus, when the pneumatic tire 1 is used at a highload, the pneumatic tire 1 is used at an increased air pressure. Whenthe vehicle equipped with the pneumatic tires 1 travels, the pneumatictire 1 rotates with the ground contact surface 3 at a portion positionedon a lower side in the ground contact surface 3 in contact with the roadsurface. The vehicle travels by transferring a driving force and abraking force to the road surface or generating a turning force due tothe friction force between the ground contact surface 3 and the roadsurface. For example, in a case where the vehicle on which the pneumatictires 1 are mounted travels on a dry road surface, the vehicle travelsmainly by transmitting a driving force or a braking force to the roadsurface or generating a turning force by a frictional force between theground contact surface 3 and the road surface. When the vehicle travelson a wet road surface, the vehicle travels in such a way that waterbetween the ground contact surface 3 and the road surface entersgrooves, such as the main grooves 30 and the lug grooves, and the waterbetween the ground contact surface 3 and the road surface is drainedthrough these grooves. Accordingly, the ground contact surface 3 iseasily grounded on the road surface, and the frictional force betweenthe ground contact surface 3 and the road surface allows the vehicle totravel as desired.

Additionally, while the vehicle is traveling, the pneumatic tire 1 issubjected to a load associated with a weight of a vehicle body,acceleration/deceleration, and turning. Accordingly, a large load actsin the tire radial direction. This load is mainly received by air filledinto the pneumatic tire 1, but is also received by the tread portion 2and the sidewall portion 8 as well as the air inside the pneumatic tire1. That is, the sidewall portion 8 transmits the load between the beadportion 10 to which the rim wheel R is fitted and the tread portion 2,and the tread portion 2 transmits the load between the sidewall portion8 and the road surface. Accordingly, the large load acts on the sidewallportion 8 and the tread portion 2 while the vehicle is traveling, andthe sidewall portion 8 and the tread portion 2 receive this load whiledeflecting mainly in the tire radial direction.

Additionally, while the vehicle is traveling, the pneumatic tire 1rotates, so the position in the ground contact surface 3 that comes intocontact with the road surface continuously moves in the tirecircumferential direction. In accordance with this, the positions in thesidewall portion 8 and the tread portion 2 deflecting by the load whilethe vehicle is traveling also move in the tire circumferentialdirection. Thus, while the vehicle is traveling, the pneumatic tire 1rotates while repeating the sequential deflection of the respectivepositions of the sidewall portion 8 and the tread portion 2 on the tirecircumferential direction.

Additionally, a projection projecting from a road surface, such as astone, is possibly present on a road surface on which the vehicletravels, and the vehicle during traveling possibly treads such aprojection by the tread portion 2 of the pneumatic tire 1. At this time,when the sidewall portion 8 and the tread portion 2 have a smalldeflection due to the high air pressure filled in the pneumatic tire 1,the pneumatic tire 1 cannot absorb the change in the shape of the roadsurface due to the presence of the projection, and the projectionpossibly penetrates the tread portion 2 of the pneumatic tire 1. Thatis, in the pneumatic tire 1 with the increased internal pressure, whenthe projection on the road surface is trodden, the small deflection ofthe sidewall portion 8 and the tread portion 2 causes the projection topenetrate the tread portion 2, possibly causing a shock burst.

In contrast, with the pneumatic tire 1 according to the present firstembodiment, the belt cover layer 15 is formed by the first covermaterial 41 and the second cover material 42, and the first covermaterial 41 and the second cover material 42 form the overlappingportion 45 that goes across the tire equatorial plane CL in the tirewidth direction, and thus a shock burst in a case where an internalpressure is increased can be suppressed. FIG. 6 is an explanatorydiagram illustrating a state in which a projection 105 on a road surface100 is trodden by the pneumatic tire 1 according to the firstembodiment. In the pneumatic tire 1 according to the first embodiment,by overlapping the portions of the first cover material 41 and thesecond cover material 42 going across the tire equatorial plane CL inthe tire width direction in the tire radial direction, the overlappingportion 45 where the belt cover materials 40 are the two layers can beformed at the position of going across the tire equatorial plane CL.This allows increasing a strength at break at or near the center in thetire width direction of the tread portion 2. Even when the projection105 on the road surface 100 is trodden at or near the center landportion 21 where a ground contact pressure is likely to increase, thepenetration of the projection 105 through the tread portion 2 can besuppressed. Accordingly, shock bursts caused by the projection 105 beingtrodden during traveling of the vehicle can be suppressed.

In addition, the first cover material 41 and the second cover material42 forming the belt cover layer 15 are disposed at the differentpositions in the tire width direction except for the portion of theoverlapping portion 45. Accordingly, the first cover material 41 and thesecond cover material 42 can be disposed by simultaneously spirallywinding the portions other than the overlapping portion 45. As a result,when the belt cover layer 15 is disposed for the purpose of improvingshock burst resistance performance, the disposition can be performedwith increased productivity. As a result, productivity can be improvedwhile a decrease in shock burst resistance performance is suppressed.

In addition, because the overlapping portion 45 is formed continuouslyfrom the first cover material 41 and the second cover material 42,separation at or near the end portion of the belt cover material 40 fromthe tread rubber layer 4 can be reduced. That is, when the belt covermaterials 40 forming the overlapping portion 45 are discontinuous withthe belt cover materials 40 forming the other portion in the belt coverlayer 15, both end portions of the belt cover materials 40 forming theoverlapping portion 45 are positioned on the outer side in the tireradial direction of the portions other than the overlapping portion 45in the belt cover layer 15. In this case, repetitive variation of a loadacting on the overlapping portion 45 along with the traveling of thevehicle possibly makes it easy for separation at or near both endportions of the belt cover materials 40 forming the overlapping portion45 to occur. In other words, the vicinities of both end portions of thebelt cover materials 40 forming the overlapping portion 45 are possiblylikely to be separated from the tread rubber layer 4.

In contrast, when the overlapping portion 45 is formed continuously fromthe first cover material 41 and the second cover material 42, the endportions of the belt cover materials 40 forming the overlapping portion45 exposed to the tread rubber layer 4 are reduced, so it is possible toreduce the separation of the vicinities of the end portions of the beltcover materials 40 from the tread rubber layer 4. As a result, it ispossible to improve shock burst resistance performance while suppressingedge separation of the overlapping portion 45.

Additionally, the overlapping portion 45 has the minimum width Wmin ofthe width W in the tire width direction of not less than 5 mm, and themaximum width Wmax of the width W in the tire width direction of notgreater than 40 mm, so it is possible to more reliably ensure a strengthof the overlapping portion 45 while suppressing an excessive increase inthe weight of the belt cover layer 15. In other words, when the minimumwidth Wmin of the overlapping portion 45 is less than 5 mm, the minimumwidth Wmin is excessively small, which possibly makes it difficult toensure the strength of the overlapping portion 45. In this case, evenwhen the overlapping portion 45 is formed, effectively improving thestrength at break at or near the center of the tread portion 2 in thetire width direction is difficult, and this possibly makes it difficultto effectively suppress the penetration of the projection 105 trodden bythe tread portion 2 through the tread portion 2. When the maximum widthWmax of the overlapping portion 45 is greater than 40 mm, the maximumwidth Wmax is excessively large, so there is a possibility that the beltcover material 40 used becomes excessively large. In this case, theweight of the belt cover layer 15 possibly excessively increases, andthe weight of the pneumatic tire 1 possibly excessively increases causedby the provision of the overlapping portion 45.

In contrast, when the minimum width Wmin of the overlapping portion 45is not less than 5 mm and the maximum width Wmax is not greater than 40mm, while the excessive increase in the weight of the belt cover layer15 is suppressed, the strength of the overlapping portion 45 can be morereliably ensured, and the strength at break at or near the center of thetread portion 2 in the tire width direction where a ground contactpressure is likely to increase can be more reliably improved. As aresult, while the increase in the weight of the pneumatic tire 1 issuppressed, shock burst resistance performance can be improved.

Since the first cover material 41 and the second cover material 42 arethe identical type, the strengths of the portions of the belt coverlayer 15 other than the overlapping portion 45 can be made uniform usingthe first cover material 41 and the second cover material 42 as themembers constituting the belt cover layer 15. As a result, a shock burstcan be suppressed while an influence on another performance, such assteering stability, is suppressed. By using the first cover material 41and the second cover material 42 of the identical type, the productionof the first cover material 41 and the second cover material 42 can beperformed simultaneously or continuously, and the productivity whenusing the first cover material 41 and the second cover material 42 asthe belt cover materials 40 can be improved. As a result, productivitycan be improved while a decrease in shock burst resistance performanceis suppressed more reliably.

The method for manufacturing the pneumatic tire 1 according to the firstembodiment includes: using the first cover material 41 and the secondcover material 42 as the belt cover materials 40, the step of spirallywinding the first cover material 41 from the position between theshoulder region Ash on the second side S2 and the tire equatorial planeCL to the shoulder region Ash on the first side S1; and the step ofspirally winding the second cover material 42 from the position betweenthe shoulder region Ash on the first side S1 and the tire equatorialplane CL to the shoulder region Ash on the second side S2. Accordingly,the first cover material 41 and the second cover material 42 can bewound simultaneously. This allows the shortening of the time taken fordisposing the belt cover layer 15, thereby ensuring enhancedproductivity.

Also, in the step of winding the first cover material 41 and the step ofwinding the second cover material 42, both are overlapped at the portionwhere the positions in the tire width direction become the identicalposition between the first cover material 41 and the second covermaterial 42 to form the overlapping portion 45. Accordingly, thestrength at break at or near the center of the tread portion 2 in thetire width direction where ground contact pressure is likely to increasecan be increased. As a result, even when the projection 105 on the roadsurface 100 is trodden by the vicinity of the center land portion 21,the penetration of the projection 105 through the tread portion 2 can besuppressed, and a shock burst caused by the tread of the projection 105during traveling of the vehicle can be suppressed. As a result,productivity can be improved while a decrease in shock burst resistanceperformance is suppressed.

The step of winding the first cover material 41 spirally winds the firstcover material 41 from the position between the shoulder region Ash onthe second side S2 and the tire equatorial plane CL to the shoulderregion Ash on the first side S1, and the step of winding the secondcover material 42 spirally winds the second cover material 42 from theposition between the shoulder region Ash on the first side S1 and thetire equatorial plane CL to the shoulder region Ash on the second sideS2. Accordingly, when the first cover material 41 and the second covermaterial 42 are wound, each of the first cover material 41 and thesecond cover material 42 can be wound from the position close to thetire equatorial plane CL to the outer side in the tire width direction.As a result, the winding positions of the first cover material 41 andthe second cover material 42 can be wound in directions away from oneanother in the tire width direction, so it is possible to more reliablysuppress an interference between devices used to wind the first covermaterial 41 and the second cover material 42. Thus, productivity can bemore reliably improved.

Second Embodiment

The pneumatic tire 1 according to the second embodiment has aconfiguration substantially similar to that of the pneumatic tire 1according to the first embodiment, but has a feature that the belt covermaterials 40 are folded back. Because the other configurations areidentical to those of the first embodiment, descriptions thereof will beomitted and the identical reference numerals are used.

FIG. 7 is a schematic view of the first cover material 41 and the secondcover material 42 of the pneumatic tire according to the secondembodiment. In the pneumatic tire 1 according to the second embodiment,similarly to the pneumatic tire 1 according to the first embodiment, thebelt cover layer 15 is formed by spirally winding the first covermaterial 41 and the second cover material 42 on the outer side of thebelt layer 14 in the tire radial direction, and the first cover material41 and the second cover material 42 form the overlapping portion 45 thatgoes across the tire equatorial plane CL in the tire width direction.

Furthermore, in the second embodiment, the belt cover materials 40 arefolded back in the tire radial direction at the shoulder regions Ash. Inother words, the step of winding the first cover material 41 spirallywinds the first cover material 41 from the inner end portion 41 apositioned on the second side S2 to the shoulder region Ash on the firstside S1, and is folded back to the outer side in the tire radialdirection at the shoulder region Ash on the first side S1. A folded backportion 41 b as a portion folded back to the outer side in the tireradial direction is spirally wound on the outer side in the tire radialdirection further than a portion of the belt layer 14 in the first covermaterial 41 wound on the outer side in the tire radial direction from aposition folded back at the shoulder region Ash to the tire equatorialplane CL.

Similarly to the second cover material 42, the step of winding thesecond cover material 42 spirally winds the second cover material 42from the inner end portion 42 a positioned on the first side S1 to theshoulder region Ash on the second side S2, and is folded back to theouter side in the tire radial direction at the shoulder region Ash onthe second side S2. A folded back portion 42 b as a portion folded backto the outer side in the tire radial direction is spirally wound on theouter side in the tire radial direction further than a portion of thebelt layer 14 in the second cover material 42 wound on the outer side inthe tire radial direction from a position folded back at the shoulderregion Ash to the tire equatorial plane CL.

Note that the folded back portion 41 b of the first cover material 41and the folded back portion 42 b of the second cover material 42 may bepositioned only in the shoulder regions Ash, or may have portionspositioned on the inner side in the tire width direction than theshoulder regions Ash. In other words, an outer end portion 41 c, whichis an end portion on the folded back portion 41 b side of the firstcover material 41, and an outer end portion 42 c, which is an endportion on the folded back portion 42 b side of the second covermaterial 42, may be positioned in the shoulder regions Ash, or may bepositioned on the inner sides in the tire width direction than theshoulder regions Ash.

Thus, the belt cover materials 40 folded back at the shoulder regionsAsh have a width in the tire width direction of the portions overlappingin the tire radial direction within a range of from not less than 5% tonot greater than 50% of a width CW in the tire width direction of thebelt cover layer 15. The width in the tire width direction of theportions overlapping in the tire radial direction in this case is atotal width of adding all of a width We1 of the folded back portion 41 bof the first cover material 41 in the tire width direction, a width We2of the folded back portion 42 b of the second cover material 42 in thetire width direction, and the width W of the overlapping portion 45 inthe tire width direction.

Similarly to the pneumatic tire 1 according to the first embodiment, inthe pneumatic tire 1 according to the second embodiment thus configured,the belt cover layer 15 is formed by spirally winding the first covermaterial 41 and the second cover material 42 on the outer side in thetire radial direction of the belt layer 14, and the first cover material41 and the second cover material 42 form the overlapping portion 45.Thus, while a decrease in shock burst resistance performance issuppressed, productivity can be improved.

In addition, since the belt cover materials 40 are folded back in thetire radial direction at the shoulder regions Ash, a force that the beltcover layer 15 constrains in the vicinity of the end portions in thetire width direction of the belt layer 14 can be increased. As a result,while the vehicle is traveling, the belt cover layer 15 can morereliably suppress an expansion of the end portions of the belt layer 14in the tire width direction to the outer side in the tire radialdirection. Accordingly, a ground contact length on both sides in thetire width direction in a contact patch shape when the ground contactsurface 3 contacts a ground can be shortened. In other words, by foldingback the belt cover materials 40 in the tire radial direction at theshoulder regions Ash, the contact patch shape can be adjusted, and theperformance during traveling, such as steering stability, can be made tothe desired performance. As a result, the desired traveling performancecan be ensured while a decrease in shock burst resistance performance issuppressed.

In addition, since the width in the tire width direction of the portionsof the belt cover materials 40 overlapping in the tire radial directionis within the range of from not less than 5% to not greater than 50% ofthe width CW of the belt cover layer 15 in the tire width direction, itis possible to more reliably ensure the strength of the overlappingportion 45 and the constraining force at or near the end portions of thebelt layer 14 by the belt cover layer 15 while suppressing the excessiveincrease in the weight of the belt cover layer 15. In other words, in acase where the width in the tire width direction of the portionsoverlapping in the tire radial direction of the belt cover materials 40is less than 5% of the width CW of the belt cover layer 15, because thewidth of the portions overlapping in the tire radial direction isexcessively narrow, the strength of the overlapping portion 45 ispossibly difficult to be ensured, and the constraining force at or nearthe end portions of the belt layer 14 by the belt cover layer 15 ispossibly difficult to be ensured. In this case, the strength at break ator near the center of the tread portion 2 in the tire width direction isless likely to be effectively improved by the overlapping portion 45,and the ground contact lengths of both sides in the tire width directionin the contact patch shape are possibly less likely to be effectivelyshortened. When the width in the tire width direction of the portions ofthe belt cover materials 40 overlapping in the tire radial direction isgreater than 50% of the width CW of the belt cover layer 15, the widthof the portions overlapping in the tire radial direction is excessivelylarge, which possibly causes the excessive increase in the weight of thebelt cover layer 15. In this case, providing the overlapping portion 45and folding back the belt cover materials 40 possibly result inexcessive increase in the weight of the pneumatic tire 1.

In contrast, when the width in the tire width direction of the portionsof the belt cover materials 40 overlapping in the tire radial directionis within a range of from not less than 5% to not greater than 50% ofthe width CW of the belt cover layer 15, it is possible to more reliablyensure the strength of the overlapping portion 45 and the constrainingforce at or near the end portions of the belt layer 14 by the belt coverlayer 15 while suppressing the excessive increase in the weight of thebelt cover layer 15. As a result, while the increase in the weight ofthe pneumatic tire 1 is suppressed, shock burst resistance performanceand running performance can be improved.

Third Embodiment

The pneumatic tire 1 according to the third embodiment has aconfiguration substantially similar to that of the pneumatic tire 1according to the first embodiment, but has a feature that portions ofthe belt cover materials 40 adjacent in the tire width direction overlapin the tire radial direction. Because the other configurations areidentical to those of the first embodiment, descriptions thereof will beomitted and the identical reference numerals are used.

FIG. 8 is a schematic view of the belt cover materials 40 included inthe pneumatic tire 1 according to the third embodiment. FIG. 9 is a planview of the belt cover material 40 illustrated in FIG. 8. Similarly tothe pneumatic tire 1 according to the first embodiment, in the pneumatictire 1 according to the third embodiment, the belt cover layer 15 isformed by spirally winding the first cover material 41 and the secondcover material 42 on the outer side in the tire radial direction of thebelt layer 14, and the first cover material 41 and the second covermaterial 42 form the overlapping portion 45 that goes across the tireequatorial plane CL in the tire width direction.

Furthermore, in the third embodiment, the belt cover material 40includes adjacent wrap portions 46 where portions adjacent in the tirewidth direction overlap in the tire radial direction by spiral winding.In other words, in the first embodiment, the spirally wound belt covermaterial 40 is spirally wound while the portions adjacent in the tirewidth direction are aligned in the tire width direction without theportions adjacent in the tire width direction of one belt cover material40 overlapping in the tire radial direction.

In contrast, in the third embodiment, in the spirally wound belt covermaterial 40, the portions adjacent in the tire width direction of onebelt cover material 40 are spirally wound while overlapped in the tireradial direction. Thus, the portions overlapped in the tire radialdirection are formed as the adjacent wrap portions 46. In the thirdembodiment, the belt cover materials 40 of both of the first covermaterial 41 and the second cover material 42 are spirally wound with theadjacent wrap portions 46. The adjacent wrap portion 46 thus formed hasa width Wb in the width direction of the belt cover material 40 in arange of from not less than 20% to not greater than 70% of a width Wa ofthe belt cover material 40.

In addition, the overlapping portion 45 has a portion where the beltcover materials 40 are three or more layers by spirally winding the beltcover materials 40 with the adjacent wrap portions 46. In other words,the overlapping portion 45 is formed by overlapping the first covermaterial 41 and the second cover material 42 in the tire radialdirection. Meanwhile, when the portions of the first cover material 41and the second cover material 42 forming the overlapping portion 45include the adjacent wrap portions 46, the belt cover materials 40 arethree or more layers at the positions of the adjacent wrap portions 46.For example, in a case where the adjacent wrap portion 46 is provided atthe portion where the overlapping portion 45 is formed in the firstcover material 41, the three layers of the belt cover materials 40,which are the two layers of the first cover materials 41 and one layerof the second cover material 42 forming the adjacent wrap portions 46,are layered in the overlapping portion 45. The same applies to a case inwhich the adjacent wrap portion 46 is provided at the portion of thesecond cover material 42 where the overlapping portion 45 is formed.

In addition, in a case where both of portions of the first covermaterial 41 where the overlapping portion 45 is formed and the portionof the second cover material 42 where the overlapping portion 45 isformed have the adjacent wrap portions 46 and the adjacent wrap portion46 of the first cover material 41 and the adjacent wrap portion 46 ofthe second cover material 42 overlap in the tire radial direction, thebelt cover materials 40 are layered in four layers. By thus providingthe adjacent wrap portion 46 at at least one of the first cover material41 or the second cover material 42, the overlapping portion 45 has theportion where the belt cover materials 40 are in three or more layers.

Similarly to the pneumatic tire 1 according to the first embodiment, inthe pneumatic tire 1 according to the third embodiment thus configured,the first cover material 41 and the second cover material 42 form theoverlapping portion 45 in the belt cover layer 15. Thus, while adecrease in shock burst resistance performance is suppressed,productivity can be improved.

Also, since the belt cover materials 40 are spirally wound with theadjacent wrap portion 46, the belt cover layer 15 can be disposed withfurther high strength. As a result, the strength at break of the treadportion 2 can be increased to a wider range by the belt cover layer 15,and a shock burst can be more reliably suppressed. In addition, thewidth Wb of the adjacent wrap portion 46 in the width direction of thebelt cover material 40 is within a range of from not less than 20% tonot greater than 70% of the width Wa of the belt cover material 40.Accordingly, a shock burst can be more reliably suppressed while theexcessive increase in the weight of the belt cover layer 15 issuppressed.

In other words, when the width Wb of the adjacent wrap portion 46 isless than 20% of the width Wa of the belt cover material 40, even whenthe adjacent wrap portion 46 is provided and the belt cover materials 40are wound, effectively increasing the strength at break of the treadportion 2 is possibly difficult compared with a case of not providingthe adjacent wrap portion 46. In this case, even when the adjacent wrapportion 46 is provided, the effect of suppressing a shock burst byproviding the adjacent wrap portion 46 is possibly difficult to beobtained. In addition, when the width Wb of the adjacent wrap portion 46is greater than 70% of the width Wa of the belt cover material 40, thewidth Wb of the adjacent wrap portion 46 is excessively large, whichpossibly causes the belt cover material 40 used to be excessively large.In this case, the weight of the belt cover layer 15 is possiblyexcessively increased, which possibly causes the excessive increase inthe weight of the pneumatic tire 1.

In contrast, when the width Wb of the adjacent wrap portion 46 is withina range of from not less than 20% to not greater than 70% of the widthWa of the belt cover material 40, while the excessive increase in theweight of the belt cover layer 15 is suppressed, the strength at breakof the tread portion 2 in the tire width direction can be increased to awider range and a shock burst can be more reliably suppressed. As aresult, while the increase in the weight of the pneumatic tire 1 issuppressed, shock burst resistance performance can be improved.

In addition, at least one of the first cover material 41 or the secondcover material 42 includes the adjacent wrap portion 46 in theoverlapping portion 45 so as to provide the portion where the belt covermaterials 40 are three or more layers. Thus, the strength of theoverlapping portion 45 can be more reliably ensured. This allows morereliably increasing the strength at break at or near the center of thetread portion 2 in the tire width direction, and allows suppressing ashock burst more reliably. As a result, it is possible to improve shockburst resistance performance more reliably.

Method for Manufacturing Pneumatic Tire and Effects

In the third embodiment as well, the first cover material 41 and thesecond cover material 42 are each wound to the outer side in the tirewidth direction from the position near the tire equatorial plane CL. Inother words, first, in the first cover material 41, the inner endportion 41 a is disposed on the second side S2, and while the adjacentwrap portion 46 is formed, the first cover material 41 is spirally woundto the shoulder region Ash side on the first side S1. Similarly, first,in the second cover material 42, the inner end portion 42 a is disposedon the first side S1 and while the adjacent wrap portion 46 is formed,the second cover material 42 is spirally wound to the shoulder regionAsh side on the second side S2.

In the case where the belt cover materials 40 are spirally wound whilethe adjacent wrap portions 46 are provided as well, the first covermaterial 41 and the second cover material 42 are each thus wound fromthe position near the tire equatorial plane CL to the outer side in thetire width direction, and thus the inner end portion 41 a of the firstcover material 41 and the inner end portion 42 a of the second covermaterial 42 can be covered with another portion of the belt covermaterial 40. As a result, the inner end portion 41 a of the first covermaterial 41 and the inner end portion 42 a of the second cover material42, which are positioned at or near the center in the tire widthdirection of the tread portion 2 where a large load is likely torepeatedly act, can be disposed away from the tread rubber layer 4. As aresult, the edge separation caused by stress concentration at a contactportion between the inner end portion 41 a of the first cover material41 and the inner end portion 42 a of the second cover material 42 andthe tread rubber layer 4 can be reduced. As a result, it is possible toimprove shock burst resistance performance while suppressing the edgeseparation of the overlapping portion 45.

MODIFIED EXAMPLES

In the above-described first embodiment, the four main grooves 30 areformed, but the number of main grooves 30 may be other than four. In thefirst embodiment described above, although the center land portion 21 ispositioned on the tire equatorial plane CL, the land portion 20 needsnot to be positioned on the tire equatorial plane CL. For example, themain groove 30 may be positioned on the tire equatorial plane CL. Whenthe main groove 30 is positioned on the tire equatorial plane CL, atleast a part of the overlapping portion 45 of the belt cover layer 15 ispreferably positioned on the inner side in the tire radial direction ofthe land portion 20 closest to the tire equatorial plane CL among theplurality of land portions 20.

Also, in the case where the belt cover materials 40 are spirally woundwhile the adjacent wrap portions 46 are provided as in the thirdembodiment, the belt cover materials 40 may be folded back in the tireradial direction at the shoulder regions Ash as in the secondembodiment. FIG. 10 is a modified example of the third embodiment, andis an explanatory diagram in a case where the belt cover materials 40are folded back at the shoulder regions Ash. As illustrated in FIG. 10,the first cover material 41 and the second cover material 42 may be eachspirally wound from the position near the tire equatorial plane CL tothe outer side in the tire width direction while the adjacent wrapportions 46 (see FIG. 9) are provided and may be folded back in the tireradial direction at the shoulder regions Ash. As a result, while thestrength at break of the tread portion 2 can be increased to a widerrange by the belt cover layer 15, the contact patch shape can beadjusted, and the performance during traveling, such as steeringstability, can be the desired performance. As a result, while thedecrease in shock burst resistance performance is more reliablysuppressed, desired traveling performance can be ensured.

Additionally, in the first embodiment described above, the portion ofthe belt cover material 40 forming the overlapping portion 45 is indirect contact with the tread rubber layer 4, but the portion of thebelt cover material 40 forming the overlapping portion 45 may be not incontact with the tread rubber layer 4. FIG. 11 is a modified example ofthe first embodiment, and is an explanatory diagram in a case where afull cover 50 is provided outside the overlapping portion 45. Forexample, as illustrated in FIG. 11, the full cover 50 disposed betweenthe shoulder regions Ash on both sides in the tire width direction maybe disposed on the outer side in the tire radial direction of the firstcover material 41 and the second cover material 42. In other words, thebelt cover layer 15 may include the full cover 50 on the outer side inthe tire radial direction of the first cover material 41 and the secondcover material 42. The full cover 50 is formed by spirally winding thebelt cover material 40 similar to the first cover material 41 and thesecond cover material 42 on the outer side in the tire radial directionof the first cover material 41 and the second cover material 42 betweenthe shoulder regions Ash on both sides in the tire width direction.

In this way, by disposing the full cover 50 on the outer side in thetire radial direction of the first cover material 41 and the secondcover material 42, the portion forming the overlapping portion 45 in thefirst cover material 41 or the second cover material 42 can be disposedaway from the tread rubber layer As a result, the edge separation causedby stress concentration at the contact portion between the inner endportion 41 a (see FIG. 3) of the first cover material 41 and the innerend portion 42 a (see FIG. 3) of the second cover material 42 and thetread rubber layer 4 can be more reliably reduced. As a result, whilethe edge separation of the overlapping portion 45 is more reliablyreduced, shock burst resistance performance can be improved.

In the first embodiment described above, the first cover material 41 isspirally wound from the position between the shoulder region Ash on thesecond side S2 and the tire equatorial plane CL to the shoulder regionAsh on the first side S1, and the second cover material 42 is spirallywound from the position between the shoulder region Ash on the firstside S1 and the tire equatorial plane CL to the shoulder region Ash onthe second side S2. However, the direction of winding the first covermaterial 41 and the second cover material 42 may be other than this. Forexample, the first cover material 41 may be spirally wound from theposition of the shoulder region Ash on the first side S1 to the positionbetween the shoulder region Ash on the second side S2 and the tireequatorial plane CL, and the second cover material 42 may be spirallywound from the position of the shoulder region Ash on the second side S2to the position between the shoulder region Ash on the first side S1 andthe tire equatorial plane CL.

Alternatively, the first cover material 41 and the second cover material42 may be wound in the identical direction in the tire width direction.For example, the first cover material 41 may be spirally wound from theposition between the shoulder region Ash on the second side S2 and thetire equatorial plane CL to the shoulder region Ash on the first sideS1, and the second cover material 42 may be spirally wound from theposition of the shoulder region Ash on the second side S2 to theposition between the shoulder region Ash on the first side S1 and thetire equatorial plane CL. It is only required that the belt cover layer15 is wound so as to ensure forming the overlapping portion 45 with thefirst cover material 41 and the second cover material 42, regardless ofthe direction of winding the first cover material 41 and the secondcover material 42.

Furthermore, the above-described first to third embodiments and modifiedexamples may be combined as appropriate. The pneumatic tire 1 forms thebelt cover layer 15 by spirally winding at least the first covermaterial 41 and the second cover material 42 on the outer side of thebelt layer 14 in the tire radial direction, and forms the overlappingportion 45 that goes across the tire equatorial plane CL in the tirewidth direction with the first cover material 41 and the second covermaterial 42. This allows improving productivity while a decrease inshock burst resistance performance is suppressed.

EXAMPLES

FIGS. 12A-12B include a table showing results of performance evaluationtests of pneumatic tires. Hereinafter, evaluation tests of theperformance of the pneumatic tire 1 described above performed onpneumatic tires of Conventional Examples and the pneumatic tires 1according to the embodiments of the present technology will bedescribed. The performance evaluation tests performed a plunger test,which is an evaluation test for shock burst resistance performance, anda test on productivity during manufacturing a tire.

The performance evaluation tests were performed using the pneumatic tire1 having the nominal size of 275/45ZR19 105Y of the tire defined byJATMA and mounted on a standard rim wheel of JATMA having a rim size of19×9.5 J. The evaluation method for each of the test items was evaluatedfor the plunger test by filling the test tire with an air pressure of aregular internal pressure, performing a plunger breakage test, inaccordance with JIS (Japanese Industrial Standard) K6302 with a plungerdiameter of 19 mm and an insertion speed of 50 mm/minute, and measuringa tire breaking energy J. The evaluation results of the plunger testshow that the greater the measured tire breaking energy J is, thesuperior a tire strength is and the superior shock burst resistanceperformance is. Note that, regarding shock burst resistance performance,even when a tire breaking energy is lower than those of ConventionalExamples 1, 2, as long as the measured tire breaking energy exceeds 94%of the tire breaking energies of Conventional Examples 1, 2, thedecrease in the shock burst resistance performance is regarded to besuppressed.

In addition, regarding productivity, a time required for winding thebelt cover materials 40 in the step of winding the belt cover materials40 during manufacturing the tire was measured. The productivity isexpressed as index evaluations of a reciprocal of the measured time withConventional Example 1 described below being assigned as 100. Largerindex values indicate shorter winding time and higher productivity.

The performance evaluation test was performed on 14 types of pneumatictires, which were pneumatic tires of Conventional Examples 1 and 2 asexamples of the conventional pneumatic tires and Examples 1 to 12 as thepneumatic tires 1 according to the embodiments of the presenttechnology. Of these, the pneumatic tire of Conventional Example 1 doesnot include the overlapping portion 45 in the belt cover layer 15. Notethat in the pneumatic tire of Conventional Example 1, the belt coverlayer 15 is formed by one belt cover material 40. In the pneumatic tireof Conventional Example 2, the belt cover layer 15 includes theoverlapping portion 45, but the overlapping portion 45 is constituted bythe single belt cover material 40, and the width W of the overlappingportion 45 in the tire width direction does not vary depending on theposition in the tire circumferential direction and has a constant width.

In contrast, in Examples 1 to 12 as examples of the pneumatic tires 1according to the embodiments of the present technology, all of the beltcover layers 15 include the overlapping portions 45, the overlappingportion 45 is constituted by the two belt cover materials 40, and thewidth W of the overlapping portion 45 in the tire width direction variesdepending on the position in the tire circumferential direction.Moreover, in the pneumatic tires 1 according to Examples 1 to 16, eachof the minimum width Wmin of the overlapping portion 45, the maximumwidth Wmax of the overlapping portion 45, presence of the adjacent wrapportion 46, and the width Wb of the adjacent wrap portion 46 to thewidth Wa of the belt cover material 40 differ.

As the result of the performance evaluation tests using these pneumatictires 1, as shown in FIGS. 12A-12B, it has been found that the pneumatictires 1 according to Examples 1 to 12 can increase productivity comparedto those of Conventional Examples 1, 2 while a decrease in the shockburst resistance performance evaluated by the plunger test is suppressedto a much greater amount than those of Conventional Examples 1, 2. Inother words, the pneumatic tires 1 according to Examples 1 to 12 and themanufacturing methods for the pneumatic tires 1 according to Examples 1to 12 can improve productivity while suppressing a decrease in shockburst resistance performance.

1. A pneumatic tire, comprising: a tread portion; a belt layer disposedin the tread portion; and a belt cover layer disposed on an outer sidein a tire radial direction of the belt layer, the belt cover layer beingformed by spirally winding band-like belt cover materials on the outerside of the belt layer in the tire radial direction around a tirerotation axis, the belt cover materials comprising a first covermaterial and a second cover material, when one side in a tire widthdirection with respect to a tire equatorial plane is defined as a firstside and another side in the tire width direction with respect to thetire equatorial plane is defined as a second side, the first covermaterial being disposed from a position between a shoulder region on thesecond side and the tire equatorial plane to a shoulder region on thefirst side, the second cover material being disposed from a positionbetween the shoulder region on the first side and the tire equatorialplane to the shoulder region on the second side, the first covermaterial and the second cover material having an overlapping portion ata position where positions in the tire width direction become positionsidentical to one another, the first cover material and the second covermaterial overlapping in the tire radial direction at the overlappingportion, and the overlapping portion has a width in the tire widthdirection that varies depending on a position thereof in a tirecircumferential direction.
 2. The pneumatic tire according to claim 1,wherein the overlapping portion has a minimum width of the width in thetire width direction of not less than 5 mm, and the overlapping portionhas a maximum width of the width in the tire width direction of notgreater than 40 mm.
 3. The pneumatic tire according to claim 1, whereinthe belt cover materials are folded back in the tire radial direction atthe shoulder regions.
 4. The pneumatic tire according to claim 1,wherein the belt cover materials have a width in the tire widthdirection of portions overlapping in the tire radial direction of withina range of from not less than 5% to not greater than 50% of a width inthe tire width direction of the belt cover layer.
 5. The pneumatic tireaccording to claim 1, wherein the belt cover materials comprise anadjacent wrap portion where portions adjacent in the tire widthdirection overlap in the tire radial direction by the spiral winding,and the adjacent wrap portion has a width in the width direction of thebelt cover materials in a range of from not less than 20% to not greaterthan 70% of a width of the belt cover materials.
 6. The pneumatic tireaccording to claim 5, wherein at least one of the first cover materialor the second cover material comprises the adjacent wrap portion suchthat the overlapping portion has a portion where the belt covermaterials are three or more layers.
 7. The pneumatic tire according toclaim 1, wherein the first cover material and the second cover materialare an identical type.
 8. A method for manufacturing a pneumatic tirethat spirally winds band-like belt cover materials on an outer side in atire radial direction of a belt layer around a tire rotation axis todispose a belt cover layer, the method comprising: using a first covermaterial and a second cover material as the belt cover materials; whenone side in a tire width direction with respect to a tire equatorialplane is defined as a first side and another side in the tire widthdirection with respect to the tire equatorial plane is defined as asecond side; spirally winding the first cover material from a positionbetween a shoulder region on the second side and the tire equatorialplane to a shoulder region on the first side; and spirally winding thesecond cover material from a position between the shoulder region on thefirst side and the tire equatorial plane to the shoulder region on thesecond side, winding the first cover material and winding the secondcover material overlap the first cover material and the second covermaterial in the tire radial direction at a portion where positions inthe tire width direction are an identical position between the firstcover material and the second cover material to form an overlappingportion, the overlapping portion having a width in the tire widthdirection that varies depending on a position thereof in a tirecircumferential direction, the first cover material and the second covermaterial overlapping in the tire radial direction at the overlappingportion.
 9. The method for manufacturing the pneumatic tire according toclaim 8, wherein the winding of the first cover material spirally windsthe first cover material from the position between the shoulder regionon the second side and the tire equatorial plane to the shoulder regionon the first side; and the winding of the second cover material spirallywinds the second cover material from the position between the shoulderregion on the first side and the tire equatorial plane to the shoulderregion on the second side.
 10. The pneumatic tire according to claim 2,wherein the belt cover materials are folded back in the tire radialdirection at the shoulder regions.
 11. The pneumatic tire according toclaim 10, wherein the belt cover materials have a width in the tirewidth direction of portions overlapping in the tire radial direction ofwithin a range of from not less than 5% to not greater than 50% of awidth in the tire width direction of the belt cover layer.
 12. Thepneumatic tire according to claim 11, wherein the belt cover materialscomprise an adjacent wrap portion where portions adjacent in the tirewidth direction overlap in the tire radial direction by the spiralwinding, and the adjacent wrap portion has a width in the widthdirection of the belt cover materials in a range of from not less than20% to not greater than 70% of a width of the belt cover materials. 13.The pneumatic tire according to claim 12, wherein at least one of thefirst cover material or the second cover material comprises the adjacentwrap portion such that the overlapping portion has a portion where thebelt cover materials are three or more layers.
 14. The pneumatic tireaccording to claim 13, wherein the first cover material and the secondcover material are an identical type.